为什么这个程序会出现浮点异常？

Question

#include <stdio.h>

int
main()
{
  int i;
  int c;
  int a[30] = { 5,  7,  11, 13,  17,  19,  23,  29,  31,  37,
                41, 43, 47, 53,  59,  61,  67,  71,  73,  79,
                83, 89, 97, 101, 103, 107, 109, 113, 127, 131 };
  for (i = 0; i < 30; i++) {
    c = (a[i] + i) / (i - 1);
    printf("Value of c is %d", c);
  }
}

I am not getting why I am facing floating point exception error in this program.

Answer 1

for(i = 0; i < 30; i++){
    c = (a[i] + i)/(i-1);

On the second iteration of this loop you divide by zero.

For historical reasons, on Unix systems integer division by zero is reported using the same signal (SIGFPE, "Floating point exception") that is used to report errors actually caused by floating-point arithmetic. This can't be changed now because too many existing programs depend on it.

(I don't know what the historical reasons actually were. They're probably something along the lines of "the PDP-11 had a floating point divide instruction but not an integer divide instruction, so the original C compiler used floating point math to implement integer divide" but I just made that up, if it's true it's by accident.)

(Ironically, on a modern CPU floating-point division by zero will usually produce a ±Inf result but not trigger a signal, unless you use fesetenv to turn on trapping.)

Answer 2

In the second iteration of the loop, i is 1, so when you divide by i-1 , you are dividing by 0.

How this would be fixed would depend on the purpose of your program.

Answer 3

在第二次迭代i = 1因此你除以 0。